Panasonic VP-7721A Manual

“8 8 -9*three digits of the frequency or output amplitude can be incremented ordecremented by the up/down keys located beneath each digit. The lowertwo digits can also be controlled by a rotary encoder. Frequency rangesare automatically switched when the numeral on the digital frequencyindicator passes through each cross point (concerned with 1599 or 16).The current range can be known by reading the range indicator (LEDs) andthe decimal point on display. The indicator displays frequencies oroutput amplitudes, whichever selected to be controlled. The display canbe switched manually, however, the setting reverts to the previous onein the following up or down keystroke .1.3 Distortion MeterDistortion meter section of the VP-7721A contains a tracking rejectionfilter which is tuned to the oscillator frequency. A multi-stagefilter circuit achieves a wide and steep frequency response,permitting signals with some frequency shift to be measured and a dis¬tortion factor of down to 0.001% to be displayed. The meter measurestotal harmonic distortion from 0.003% full scale to 100% full scale inten ranges that can be switched automatically.Since the distortion meter utilizes the Ratio Calculating Method*, theoperator is released from the tedious set-level procedure. The ampli¬tude of the input signal is monitored on the other meter. If theanplitude deviates from the range suitable for measuring the distortionfactor, an annunciator lights. The distortion meter can be adapted forautomatic range switching, in which the appropriate range is automati¬cally selected. Figure 1-2 shows a conceptional block diagram of theVP-7721A.4rgo04O1-2* A conventional distortion meter determines distortion factors bydividing the (amplitude of the signal which excludes the fundamentalcomponent) by the (total signal amplitude)-It requires that the total signal amplitude be set to a referencevalue (set-level) before the distortion factor can be read directlyfrom the amplitude of the signal which excludes the fundamentalcomponent. However, direct reading of the calculated ratio betweenthese two types of signals eliminates the need of the set-level proce¬dure. It was developed by Matsushita and has been used in the VP-7702series and later.